Shell morphology. Measurements up to 9x5 mm, with 5 whorls. General shape rather elevated. Whorls distinctly flattened, giving to the spire a conical outline. Surface smooth and glossy, with indistinct growth lines. Shell material translucent, tending to become porcellanous in gerontic specimens. Aperture oval. Inner lip closely appressed without any umbilicus or chink in adult specimens. Colour pattern. Colour pattern includes a single tone of reddish to reddish-orange markings, commonly accompanied by small opaque-white patches. Background is vitreous to whitish. The most common design consists of a series of flames or clusters of lineoles under the suture, the remainder of the whorl bearing closely and regularly-displayed dots alternating with spiral bands of crescent-like patches. Occasionally these dots merge into oblique lines on part of the shell (particularly the base of the last whorl) thus approximating some designs of T. pullus picta. Exceptional individuals may be entirely red, or white, or covered with regularly-parallel, oblique red lines.

Species of intermediate form between pullus pullus and speciosa. Mainly it is distinguishable due to its fragility and semi-transparence. Slim in outline, whorls flat-convex, suture not much broad. Last whorl is 70% of total height and it is subangular at the base. Aperture small, circular in form, columella arched, external lip sharp and showing glimpses of external colouring. Umbilicus missing. Colour pattern quite variable but less bright compared with the other two species, even if ornamentation is similar and it is made by running spiral bands and by spots red and white in colour alternate to other ones made by small pits red in colour brought closer. There were described, mainly by Monterosato (1884), many varieties in colour of no taxonomic value. Average measures of adult specimens are around 10 mm in height.

T. tenuis differs from T. pullus pullus by
(1) higher spire;
(2) flatter whorls; and
(3) predominance of dotted pattern as described above, without any important extension of vertical flames.

It differs from T. pullus picta by
(1) higher spire; and
(2) predominance of the dotted pattern over the oblique lines.
As already stated, there are transitional forms between T. tenuis and T. pullus picta in the westernmost Mediterranean and the Straits of Gibraltar area. In extensive Mediterranean areas (e.g. Mediterranean coast of France, Italy, Corsica, Tunisia) the existence of T. tenuis together with T. pullus pullus is well documented and these are clearly separable in sympatric populations.

The name T. hoberti stands for small forms, grossly similar to T. tenuis but lacking the most typical dots-and-blotches pattern and high conical spire of the latter (Brusina, 1864; Monterosato 1883, 1884). The description of Phasianetla pulla (L.) var. hoberti appears in the same paper (Brusina, 1864) as that of Phasianetla crassa (which is T. pullus pullus as intended here). It is clear from Brusina's descriptions and comparisons that his conception of T. pullus applies to what we call T. tenuis.

This form is reported throughout most of the Mediterranean. It may occur, with morphologies typical and transitional to T. pullus picta, in southern Spanish Atlantic (Cadiz, Puerto de Santa Maria) and in the western Alboran Sea. Habitat is infralittoral, and generally restricted to sheltered localities.

Habitat: it lives on coralligenous bottoins and on laminariae in the infralittoral zone. Distribution: common all over the Mediterranean.